Man-made ponds behind arsenic in Bangladesh water

London, Nov 16 (ANI): MIT researchers claim to have tracked down the origin of dissolved arsenic in Bangladesh's drinking water.

The research team led by Rebecca Neumann and Khandakar Ashfaque have found that human alteration to the landscape, the construction of villages with ponds, and the adoption of irrigated agriculture are responsible for the current pattern of arsenic concentration underground.

In 2002, a study led by Charles Harvey, the Doherty Associate Professor of Civil and Environmental Engineering at MIT showed that microbial metabolism of organic carbon was mobilizing the arsenic off the soils and sediments, and that crop irrigation was almost certainly playing a role in the process.

The new study showed that man-made ponds built for the purpose of providing soil to build up villages for flood protection are the source of the organic carbon.

The carbon settles to the bottom of the ponds, then seeps underground where microbes metabolize it.

This creates the chemical conditions that cause arsenic to dissolve off the sediments and soils and into the groundwater.

The researchers also found that rice fields irrigated with arsenic-laden water actually serve to filter out much of the arsenic from the water system.

"Our research shows that water from the ponds carries degradable organic carbon into the shallow aquifer. Groundwater flow, drawn by irrigation pumping, transports that pond water to the depth where dissolved arsenic concentrations are greatest and where it is then pumped up into the irrigation and drinking wells," Nature quoted Harvey as saying.

"The other interesting thing we found is that the rice fields are a sink of arsenic - more arsenic goes in with the irrigation water than comes out in the groundwater," he added.

"When we compared the chemical signatures of the different water sources in our study area to the signatures of the aquifer water, we saw that water with high arsenic content originates from the human-built ponds, and water with lower arsenic content originates from the rice fields," said Neumann.

"It's likely that these same processes are occurring at other sites, and it suggests that the problem could be alleviated by digging deeper drinking water wells below the influence of the ponds or by locating shallow drinking wells under rice fields," Neumann added.